- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Effects of Ge substrate on the structural and optical conductivity parameters of Bi2O3 thin films
摘要： In this article the structural, optical and dielectric properties of a 200 nm thick Bi2O3 thin films which are deposited onto amorphous germanium substrate are reported. Both of the Ge and Bi2O3 thin films are prepared by the thermal evaporation technique under vacuum pressure of 10^-5 mbar. Bi2O3 thin films are found to prefer the monoclinic nature of structure with larger values of microstrain, dislocation density, stacking faults and smaller grain sizes upon replacement of the glass substrate by germanium. Optically, significant redshift in the energy band gap is observed when the films are grown onto Ge. The Ge/Bi2O3 heterojunctions exhibit a conduction and valence band offsets of value of 0.81 and 1.38 eV, respectively. In addition to the enhancement in the dielectric constant near the IR region, the Drude-Lorentz modeling of the Ge/Bi2O3 heterojunctions has shown remarkable effect of the Ge substrate on the optical conductivity parameters of Bi2O3. Particularly, the drift mobility increased by about one order of magnitude, the free hole density decreased by ~24 times and the plasmon frequency ranges extended from 5.21 to 11.0 GHz to 2.59–12.80 GHz when germanium substrate is used. The optical features of the heterojunction nominate it for visible light communication technology.
关键词： Ge/Bi2O3,Band offsets,X-ray,Heterojunction,Plasmon,Dielectric
更新于2025-09-23 15:23:52
-
Interfacial structure of SrZr <sub/><i>x</i> </sub> Ti <sub/>1?</sub><sub/><i>x</i> </sub> O <sub/>3</sub> films on Ge
摘要： The interfacial structure of SrZrxTi1?xO3 films grown on semiconducting Ge substrates is investigated by synchrotron X-ray diffraction and first-principles density functional theory. By systematically tuning the Zr content x, the effects of bonding at the interface and epitaxial strain on the physical structure of the film can be distinguished. The interfacial perovskite layers are found to be polarized as a result of cation-anion ionic displacements perpendicular to the perovskite/semiconductor interface. We find a correlation between the observed buckling and valence band offsets at the SrZrxTi1?xO3/Ge interface. The trends in the theoretical valence band offsets as a function of Zr content for the polar structures are in agreement with reported X-ray photoelectron spectroscopy measurements. These results have important implications for the integration of functional oxide materials with established semiconductor based technologies.
关键词： synchrotron X-ray diffraction,density functional theory,valence band offsets,SrZrxTi1?xO3 films,Ge substrates,interfacial structure
更新于2025-09-23 15:21:01
-
Analysis of Processa??Dependent Electrical Properties of Silicon Heterojunction Solar Cells by Quantum Efficiency and Temperaturea??Dependent Current Densitya??Voltage Measurements
摘要： Amorphous silicon–crystalline silicon (a-Si:H/c-Si) heterojunction solar cells are fabricated by infrared (IR) radiative or resistive preheating of silicon wafers before the a-Si:H layers deposition. The cells with IR radiative or resistive preheating lead to without S-shape (WoS) or with S-shape (WS) in their light current density–voltage (J–V) characteristics, respectively. The Suns-Voc analysis shows no front/back metal contact barriers for minority carriers in both cells. The light- and voltage-bias-dependent quantum efficiencies of the WS cell show the hindrance of carrier collection at the a-Si:H/c-Si interface due to the band offset, whereas more defective a-Si:H layers are observed in the WoS cell. The WS and WoS cells’ temperature-dependent dark J–V characteristics reveal that the carrier transport is through tunnel-assisted recombination and tunneling, respectively. The IR preheating of wafers results in the reduction of the bandgap of a-Si:H and facilitates for minimizing the band offset at the interface, whereas, the resistive heating shows the relatively better a-Si:H/c-Si interface passivation.
关键词： S-shapes,heterojunctions,quantum efficiencies,amorphous silicon,band offsets,silicon solar cells
更新于2025-09-19 17:13:59
-
Assessing the roles of Cu- and Ag-deficient layers in chalcopyrite-based solar cells through first principles calculations
摘要： Chalcopyrites are a demonstrated material platform for realizing efficient thin-film photovoltaics, with the most well known Cu(In,Ga)Se2 (CIGS)-based solar cells exceeding 23%. Several factors, including flexibility in tuning the absorber bandgap, enhanced surface treatments, and the electrically benign nature of common defects are responsible for the existing high performance and future promise in chalcopyrite-based photovoltaic devices. The introduction of Cu-poor phases (also known as ordered-vacancy compounds or OVCs) between the absorber and buffer layers in CIGS solar cells is known to enhance device performance; however, the overall properties and role of OVCs remain poorly understood. Using first principles calculations based on the density functional theory with screened hybrid functionals, we explore the electronic structure and stability of OVCs and their band offsets with defect-free chalcopyrite layers in Cu- and Ag-based compounds (ABX2 where A ? Cu, Ag; B ? In, Ga, Al; and X ? S, Se). Using AB3X5 and AB5X8 stoichiometries as model OVC systems, we report on the variation of the bandgap with the A/B ratio and discuss the trends in other Cu- and Ag-based chalcopyrites beyond CuInSe2. We find that the valence and conduction bands are lower in energy in OVCs with respect to the parent ABX2 chalcopyrite owing to a reduced p–d interaction between X and A atoms. We additionally perform device-level simulations to assess the implications of the results, finding that the valence band offsets of OVCs are favorable, while the conduction band offsets of chalcopyrites beyond CuInSe2-based absorbers may be detrimental in conventional solar cell device designs.
关键词： solar cells,density functional theory,chalcopyrites,band offsets,ordered-vacancy compounds
更新于2025-09-19 17:13:59
-
Plasma enhanced chemical vapor deposition of SiO <sub/>2</sub> and SiN <sub/>x</sub> on AlGaN: Band offsets and interface studies as a function of Al composition
摘要： In this work, the authors characterized the interface of plasma enhanced chemical vapor deposition (PECVD) dielectrics, SiO2 and SiNx with AlGaN as a function of Al composition. SiO2 is found to exhibit type I straddled band alignment with positive conduction and valence band offsets for all Al compositions. However, the interface Fermi level is found to be pinned within the bandgap, indicating a significant density of interface states. Hence, SiO2 is found to be suitable for insulating layers or electrical isolation on AlGaN with breakdown fields between 4.5 and 6.5 MV cm?1, but an additional passivating interlayer between SiO2 and AlGaN is necessary for passivation on Al-rich AlGaN. In contrast, Si-rich PECVD SiNx is found to exhibit type II staggered band alignment with positive conduction band offsets and negative valence band offsets for Al compositions <40% and type I straddled band alignment with negative conduction and valence band offsets for Al compositions >40% and is, hence, found to be unsuitable for insulating layers or electrical isolation on Al-rich AlGaN in general. In contrast to passivating stoichiometric LPCVD Si3N4, no evidence for interface state reduction by depositing SiNx on AlGaN is observed.
关键词： PECVD,band offsets,SiO2,AlGaN,interface studies,Al composition,SiNx
更新于2025-09-09 09:28:46
-
Energy Band Gap Modulation in Nd-doped BiFeO <sub/>3</sub> /SrRuO <sub/>3</sub> Heteroepitaxial for Visible Light Photoelectrochemical Activity
摘要： The ability of band offsets at multiferroic/metal and multiferroic/electrolyte interfaces in controlling charge transfer, and thus alters the photoactivity performance has sparked significant attention in solar energy conversion applications. Here, we demonstrate that the band offsets of the two interfaces play the key role in determining charge transport direction in a downward self-polarized BFO film. Electrons tend to move to BFO/electrolyte interface for water reduction. Our experimental and first-principles calculations reveal that the presence of neodymium (Nd) dopants in BFO enhances the photoelectrochemical performance by reduction of the local electron-hole pair recombination sites and modulation of the band gap to improve the visible light absorption. This opens a promising route to the heterostructure design by modulating the band gap to promote efficient charge transfer.
关键词： density functional theory (DFT),heterojunction band offsets,charge transfer,Nd-doped BiFeO3,photoelectrochemical (PEC)
更新于2025-09-04 15:30:14
-
Effect of Deposition Method on Valence Band Offsets of SiO <sub/>2</sub> and Al <sub/>2</sub> O <sub/>3</sub> on (Al <sub/>0.14</sub> Ga <sub/>0.86</sub> ) <sub/>2</sub> O <sub/>3</sub>
摘要： There are often variations in reported valence band offsets for dielectrics on semiconductors and some of the reasons documented include metal or carbon contamination, interfacial disorder, variations in dielectric composition, thermal conditions, strain, and surface termination effects. In this paper we show that there are differences of up to 1 eV in band alignments for the common gate dielectrics SiO2 and Al2O3 on single crystal (Al0.14Ga0.86)2O3, depending on whether they are deposited by sputtering or Atomic Layer Deposition. In the case of Al2O3, this changed the band alignment from nested (type I) to staggered gap (type II). The valence band offset at each heterointerface was measured using X-Ray Photoelectron Spectroscopy and was determined to be ?0.85 ± 0.15 eV for sputtered Al2O3 and 0.23 ± 0.04 eV for ALD Al2O3 on β-(Al0.14Ga0.86)2O3, while for SiO2 it was 0.6 ± 0.10 eV for sputtered and 1.6 ± 0.25 eV for ALD. These results are consistent with recent results showing that the surface of Ga2O3 and related alloys are susceptible to severe changes during exposure to energetic ion environments.
关键词： Al2O3,(Al0.14Ga0.86)2O3,SiO2,valence band offsets,Atomic Layer Deposition,X-Ray Photoelectron Spectroscopy,sputtering
更新于2025-09-04 15:30:14